JPH04366755A - Surface defect inspection device - Google Patents

Abstract

PURPOSE:To provide a method and device for inspecting surface defects whereby defects on work surfaces such as flaws and pinholes can be inspected with high accuracy. CONSTITUTION:A surface defect inspection device is provided with a light source 1 for illuminating work surfaces with light, an image pickup device 2 for receiving the light applied by the light source and reflected back, and a defect detection circuit 4 for detecting surface defects from the density of images picked up by the image pickup device 4. A red-light-emitting diode is used as the light source 1. Thereby the photosensitivity of the image pickup device 2 is enhanced and the defect detection sensitivity of the device is enhanced accordingly.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspection apparatus for inspecting the presence or absence of surface defects on a workpiece such as an aluminum (including its alloy) magnetic disk substrate.

0002

[Prior Art and Problems to be Solved] For example, aluminum magnetic disk substrates are required to have a high level of surface precision such as a mirror surface or a near-mirror surface due to its quality, and are subject to local surface defects such as scratches, pinholes, and blisters. It is required that there be no For this reason, in the manufacturing process of aluminum magnetic disk substrates, which are generally produced through various processes such as precision cutting, polishing, plating, and polishing, the presence or absence of surface defects is inspected after the completion of a predetermined process or after the completion of all processes. things are being done.

[0003] Conventionally, surface defect inspection as described above has been mainly carried out by visual inspection using the naked eye of an inspector, but recently, surface defect inspection methods and devices have been developed that detect defects by optical methods instead of manually. have been proposed (for example, JP-A-62-269049, JP-A-63-42453, etc.)
. However, such conventional surface inspection methods and devices determine not only the presence or absence of defects, but also various defect information such as defect type, location, and size. However, the structure is complicated and it takes a relatively long time to obtain test results.

Therefore, the present inventors have previously proposed a surface defect inspection device that can quickly and reliably inspect the presence or absence of surface defects on aluminum magnetic disk substrates, etc.
No. 8659). This surface defect inspection device includes a light source that irradiates light onto the surface of a workpiece, an imaging device that receives the reflected light of the light irradiated by the light source, and the presence or absence of surface defects based on the density of the image taken by the imaging device. The presence or absence of surface defects can be quickly detected with a simple configuration.

However, as aluminum magnetic disks and the like become smaller and more dense, it is expected that even with the above-mentioned surface inspection equipment, it will not be possible to inspect minute surface defects, making it difficult to detect defects. Further improvement of the limit is required.

The present invention has been made in view of these demands, and is a surface defect inspection device that increases the detection sensitivity of surface defects on workpieces such as aluminum magnetic disk substrates and is capable of detecting even smaller defects. The purpose is to provide.

[0007]

[Means for Solving the Problems] The above object is to provide a light source that irradiates light onto the surface of a workpiece, an imaging device that receives reflected light of the light irradiated by the light source, and an image taken by the imaging device. The present invention is achieved by a surface defect inspection apparatus including a surface defect detection apparatus for detecting the presence or absence of surface defects based on shading, and characterized in that a red light emitting diode is used as the light source.

[0008]

[Operation] The operation of the present invention is shown with reference to FIG. 1. Intermittently emits light from the light source (1) toward the aluminum magnetic disk substrate (A), and in synchronization with the emission, the substrate (A)
The imaging device (2) receives specularly reflected light from the substrate and captures an image of the substrate surface. The specularly reflected light received by the imaging device (2) enters each pixel of the imaging device (2), and gradation information corresponding to the amount of incident light is output. Therefore, when there is a defect such as a scratch on the surface of the substrate (A), the irradiated light from the light source (1) is diffusely reflected by the defect, and as a result, the amount of specularly reflected light incident on the corresponding pixel is reduced, and the specularly reflected light is This creates a difference in output for other pixels that properly receive light. Since a red light emitting diode is used as the light source (1), the imaging device (2)
The light-receiving sensitivity of the camera is improved, and clearer gradation information can be obtained. A signal from the imaging device (2) is input to a defect detection circuit (4). The defect detection circuit (4) compares the input gray level signal of each pixel with the gray level reference signal set to a predetermined level by the gray level setter (5), and if the input signal is smaller, the surface It is determined that there is a defect, and if the input signal is larger, it is determined that there is no defect, thereby detecting the presence or absence of a defect.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained based on an embodiment in which the present invention is applied to an apparatus for inspecting surface defects of an aluminum magnetic disk substrate as a workpiece.

In FIG. 1, (A) is an aluminum magnetic disk substrate as a workpiece, and a light beam is directed obliquely toward the surface of the magnetic disk substrate (A) on the outside and diagonally above the magnetic disk substrate (A). A light source (1) for irradiation is arranged. A red light emitting diode is used as the light source (1), and is designed to emit light intermittently at predetermined timing. Further above the substrate (A), an imaging device (2) is arranged at a position where it can receive the specularly reflected light of the light irradiated from the light source (1) onto the magnetic disk substrate (A). This imaging device (2) receives specularly reflected light from the substrate (A) and takes an image of the surface of the magnetic disk substrate,
In this embodiment, a CC is used as a preferable imaging device (2).
A D camera is used. The imaging surface of the imaging device (2) is composed of a plurality of pixels, and the substrate (A
) An electrical signal corresponding to the amount of specularly reflected light is output for each pixel as image gradation information. Therefore, if there are defects such as scratches on the substrate surface,
Since the reflected light is scattered by the defect, the amount of specularly reflected light incident on a specific pixel is reduced compared to when there is no defect, and this is output as a difference in the magnitude of the electrical signal. ing. In this way, in this example, the substrate (
The so-called bright field method in which the specularly reflected light from A) is directly received by the imaging device (2) is adopted for the following reason. That is, in the bright field method, when the irradiated light is diffusely reflected due to a defect on the substrate surface, the light that is diffusely reflected and does not enter the imaging device (2) remains as a decrease in light intensity and is recognized by the imaging device. In the dark field method, which receives diffused reflection, it is difficult to receive all of the diffusely reflected light, and if this is attempted, the apparatus becomes complicated. For this reason, the bright field method has better sensitivity to increases and decreases in the amount of light due to surface defects, which in turn increases the reliability of defect detection.

By the way, in the present invention, as mentioned above, a red light emitting diode is used as the light source (1). Here,
A red light emitting diode is one that emits red light at a wavelength of about 6400 to 7700 angstroms. The reason for using such a red light emitting diode as a light source is as follows. In other words, it is presumed that the light receiving sensitivity of the imaging device (2) is highest in the emission wavelength range of the red light emitting diode, and therefore it is possible to obtain clear shading information of the image, which in turn allows even smaller defects to be detected. This is because it can be detected. Further, by using a light emitting diode, the light source can be made smaller and have a longer lifespan, and the amount of light and the timing of light emission can be easily controlled. Note that the material, structure, etc. of the red light emitting diode are not particularly limited.

[0012] The signals for each pixel output from the imaging device (2) based on the light from the light source (1) are then electrically processed. An example of this processing circuit is also shown in FIG. In FIG. 1, (3) is a video board as an input unit that receives a signal from an imaging device (2), and (4) is a defect detection circuit. The defect detection circuit (4) is connected to the video board (3).
), the input signal for each pixel corresponding to the shading of the image is compared with the shading reference signal set to a predetermined level by the shading level setter (5), and the input signal is determined. If the input signal is smaller, it is determined that there is a surface defect, and if the input signal is larger, it is determined that there is no defect, thereby detecting the presence or absence of a defect. Here, the density reference signal set by the density level setting device (5) is directly related to the presence or absence of defects, and depending on how it is set, the criteria for determining the presence or absence of defects can be made more or less strict, and the required quality can be met. The setting level can be changed as desired.

(6) is a counting circuit that counts the number of pixels determined to be defective by the defect detection circuit (4). Further, (7) is a comparison circuit that compares the number of pixels with surface defects counted by the counting circuit (6) and the defect number setting value set in advance as an allowable value by the defect number setting device (8). If the number of pixels with surface defects is greater than a set value, it is determined to be a defective product, and if it is less than a set value, it is determined to be a good product. Therefore, the defect number setting value set in advance to the allowable value by the defect number setting device (8) is
), and depending on the setting, the acceptance criteria can be made more or less strict, and the number of settings can be changed arbitrarily depending on the required quality.

[0014] (9) is a display device that displays the determination result of the comparator circuit (7) using a lamp or the like.

Next, a method for inspecting the surface defects of an aluminum magnetic disk substrate (A) using the apparatus shown in FIG. 1 will be explained. First, the light source (1) emits light intermittently toward the magnetic disk substrate (A), and in synchronization with the light emission, the substrate (
The specularly reflected light from A) is received by the imaging device (2) and an image of the substrate surface is taken. The specularly reflected light enters each pixel of the imaging device (2), and gradation information corresponding to the amount of incident light is output. Therefore, when there is a defect such as a scratch on the surface of the substrate (A), the irradiated light from the light source (1) is diffusely reflected by the defect, and as a result, the amount of light incident on the corresponding pixel is reduced, and the specularly reflected light is This produces a difference in output for other pixels that are properly received.

[0016] The signal from the imaging device is sent to the video board (3).
The signal is inputted to the defect detection circuit (4) via. The defect detection circuit (4) compares the input gray level signal of each pixel with the gray level reference signal set to a predetermined level by the gray level setter (5), and if the input signal is smaller, the surface It is determined that there is a defect, and if the input signal is larger, it is determined that there is no defect, thereby detecting the presence or absence of a defect. This detection result is sent to a counting circuit (6), and the number of pixels determined to be defective is counted by the counting circuit (6).

Next, the counting result of the counting circuit (6) is input to the comparing circuit (7), and the number of pixels with surface defects and the defect number setting value set in advance to an allowable value by the defect number setting device (8) are input. are compared. As a result, if the number of pixels with surface defects is greater than the set value, the magnetic disk is determined to be defective, and if it is less, it is determined to be good. The determination result is displayed on the display device (9), and the board is judged to be good or bad.

As described above, according to the present invention, since the presence or absence of a defect on the substrate surface is detected based on the density of each pixel of the imaging device, the detection accuracy can be further improved by enlarging and photographing the inspection surface. . For this purpose, the surface of the aluminum magnetic disk substrate (A) is divided into multiple micro inspection areas,
It is desirable to take an enlarged image of each inspection area using an imaging device to detect the presence or absence of surface defects. As a more specific method, as shown in FIG. 2, by fixing the imaging device (2) at a predetermined position and rotating the disk substrate (A) in the circumferential direction, the substrate surface is first formed into a circumferential band shape. Continuously inspect. The rotation speed should be set in consideration of the imaging timing so that no uninspected area is formed in the circumferential direction. In this embodiment, a 3.5-inch type magnetic disk substrate (A) having an outer diameter of 95 mm and an inner diameter of 25 mm is inspected by dividing the substrate surface into 120 inspection areas in the circumferential direction. After the substrate (A) is rotated once in this manner, the imaging device (2) is moved radially by a predetermined width step as shown by the arrow in FIG. 2, and the next adjacent area is continuously inspected in a circumferential band shape. In this case, in order to maintain an appropriate positional relationship between the imaging device (2) and the light source (1), it is necessary to move the light source (1) at the same time as the imaging device (2). The moving distance of the imaging device (2) in the radial direction should be set so that no uninspected area is formed in the radial direction. is divided into four parts and moved in four steps. The number of divisions in the circumferential direction and the radial direction is appropriately determined depending on the size of the detected defect depending on the purpose and quality. Further, the inspection time for one substrate is determined by the number of divided inspection areas, the light emission cycle of the light source (1), the idle time required for moving the imaging device (2), and the like. For example, when the light emission period of the light source (1) is 1/60th of a second, if the 3.5-inch type board is divided into 120 parts in the circumferential direction and 4 parts in the radial direction, approximately
One side of the board can be inspected in about 15 seconds. In this way, by fixing the imaging device and rotating the aluminum magnetic disk substrate, the surface of the substrate is continuously inspected in a circumferential band shape, and the imaging device is moved stepwise in the radial direction for each rotation of the substrate. When this configuration is adopted, the substrate surface can be divided into micro-inspection areas and these can be inspected in an enlarged manner, making it possible to smoothly detect defects with even higher precision.

Furthermore, as shown in FIG. 3, the imaging device (2) may be arranged on the circumference of the substrate at equal positions in the radial direction. In such a case, there is no need to move the imaging device (2) step by step, and the inspection can be completed with one revolution of the substrate (A), thereby shortening the inspection time. In this case as well, it is necessary to arrange each imaging device so that an uninspected area is not formed in the radial direction. In this way, when a plurality of imaging devices are fixed corresponding to each of the plurality of divided positions in the radial direction of an aluminum magnetic disk substrate and the substrate is rotated, there is no need to move the imaging devices in steps, and one rotation of the substrate is eliminated. The inspection can be completed at the same time, thereby shortening the inspection time.

As explained above, according to the apparatus according to the illustrated embodiment, the defect detection sensitivity is increased by the irradiation of light from the light source (1) using a red light emitting diode, and the bright field detection According to the method, the imaging device (2) receives the specularly reflected light of the light irradiated toward the substrate (A), so it can directly detect the decrease in the amount of received light when the irradiated light is diffusely reflected by a surface defect, which improves the accuracy. High density information can be obtained, and defect detection accuracy can be further improved.

[0021]

Effects of the Invention As described above, the present invention has an image pickup device that receives reflected light from light irradiated onto the surface of a workpiece such as an aluminum magnetic disk substrate, and photographs an image of the substrate surface. The presence or absence of surface defects is detected from the shading of the surface.
The presence or absence of surface defects can be quickly detected with a simple configuration. Moreover, since a red light emitting diode is used as a light source, the light receiving sensitivity of the imaging device can be improved, highly accurate grayscale information can be obtained, and defect detection accuracy can be improved. Moreover, by using a light emitting diode, the light source can be made smaller and have a longer lifespan, and the amount of light and the timing of light emission can be easily controlled. Incidentally, in the surface defect inspection apparatus shown in Fig. 1, three types of light sources (1), a red light emitting diode, a green light emitting diode, and a strobe, were used, and other conditions were set the same, and the surface was inspected on an aluminum magnetic disk substrate. As a result, the sizes of detectable defective pits on the disk surface were as shown in Table 1.

[0022]

[Table 1]

From the results shown in Table 1 above, it was confirmed that defect detection sensitivity could be increased by using a red light emitting diode as a light source.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a surface defect detection device according to the present invention.

FIG. 2 is a schematic plan view for explaining a method of inspecting the surface of an aluminum magnetic disk substrate by dividing it into circumferential and radial inspection areas.

FIG. 3 is a schematic plan view for explaining another method of inspecting the surface of an aluminum magnetic disk substrate by dividing it into circumferential and radial inspection areas.

[Explanation of symbols]

A... Aluminum magnetic disk substrate (work) 1... Light source (red light emitting diode) 2... Imaging device 4... Defect detection circuit

Claims (1)

[Claims] [Claim 1] A light source (1
), an imaging device (2) that receives the reflected light of the light emitted by the light source, and a defect detection circuit (4) that detects the presence or absence of surface defects from the density of the image taken by the imaging device.
), the light source (1)
) A surface defect inspection device characterized in that a red light emitting diode is used as a red light emitting diode.